This past week, FOP officially kicked off its Geologic City project. On Wednesday we took part in a soggy walk with other members of the American Museum of Natural History and charted what was new geologic territory for FOP in the far reaches of Northern Manhattan. This walk was our first geologist-lead event and we couldn’t have started with a more knowledgeable urban geologist than Sidney Horenstein.

tourees inspect a monument marking the purchase of Manhattan from the Lenape in 1626

The AMNH walk included Inwood Hill and Fort Tryon Park. Both are home to major geologic formations in the upper west corner of the island. Inwood Hill Park also boasts the last natural forest and salt marsh in Manhattan.

A rock slide in Inwood Hill Park, induced by glacial activity

We walked alongside rocky outcroppings and passed through forests that more resembled the Pacific Northwest than our familiar New York City. Our group was alone in these forests, putting us in awe of the fact that we were also on an island hosting almost 2 million inhabitants tightly packed within 23 square miles of land.

Sidney was a wealth of references, geologic data, Revolutionary War history, and local folklore. As we tried to keep up with both his brisk pace and his flood of facts, we managed to process some striking bits of information. Manhattan schist, part of the solid bedrock support responsible for making skyscrapers possible on Manhattan, became metamorphic rock about 450 million years ago. The schist is the second oldest component of New York City’s bedrock, after Fordham Gneiss. The schist became part of Manhattan island during continental collision between the floor of the predecessor to the Atlantic Ocean, the Iapetus Ocean, and what would later be known as the East Coast of North America.

a tree finds ways to root itself upon the mighty Manhattan schist

Both Inwood Hill Park and Fort Tyron Park display fantastic Pleistocene induced formations. Glaciers scoured the entire island over 10,000 years ago, and their marks are still clearly visible in both parks today. Our tour included the City’s largest glacial pothole, carved when pieces of rock, swirled by turbulent waters, drilled holes into the surrounding stone.

this pothole in Fort Tyron park was partially destroyed to make room for the nearby path

Sidney reminded us that Manhattan is a geologically active city today, and everyday. Several major fault lines crisscross the island, and we took a close look at the Dyckman Street fault along one of the trails in Fort Tyron.

rock upturned nearly 90 degrees at the Dyckman Street fault

geologic water fountain in Fort Tyron park (not an official point of interest on the tour)

Hudson River looking north

Our tour ended with a reminder that the Hudson River is the southernmost glacial fjord in the Northern Hemisphere.

Under last weekend’s much improved weather conditions, we set out again to begin our visual research on sites that might be included in the Geologic City field guide. This time, we weren’t seeking rocks in their “natural” environment. Instead, we sought out geologic materials that have been remixed and appropriated by human innovation, desire, and design – and now give distinct form to the City’s architecture and infrastructure.

On the way to Prospect Park we passed massive stacked rows of Triassic sandstone. These solid blocks (literally) of geology are installed on the streets as the City’s iconic “brownstones.” This rock is 250 to 200 million years old–that’s pre-dinosaur. Brownstones are one of the most common buildings in Park Slope, but we typically forget that while inhabiting such spaces, we’re living inside the materiality of deep time.

Brooklyn brownstones

a Prospect Park panther

Upon arrival at Prospect Park we were greeted by two panthers who guard the Third Street entrance. For almost a decade, we’ve passed by these sculptures and this week, we finally took the time to track down some information about where they came from and what geologic materiality composes them. The panthers were created by artist Alexander Phimister Proctor, famous for his sculptures of animals and American Western themes. A model for the north panther was first displayed at the entrance to the Paris Exposition in 1900. The Prospect Park panthers date to 1898 and were created at the Thiebaut Freres foundry in Paris. Today, like all sculptures and monuments in the city, they are managed by NYC Parks and Recreation.

The sculptures are not made of rock, but of bronze, a metal alloy consisting primarily of copper. This is where rocks and the elements that compose them get differentiated. It’s also where our research for Geologic City got technical. There are currently 118 known elements. Ninety four, including copper, occur naturally on Earth. These “natural” elements are the results of various forms of “nucleosynthesis“–processes of “breakdown” such as nuclear fission, alpha decay, cluster decay, and cosmic ray spallation. These 94 natural elements were created in stars and supernovae. Later, they coalesced into the Earth.

As a natural element that “came from” nucleosynthesis in stars and supernovae, copper has no time of origin in the geologic timescale. Unlike geologic materialities formed by, say, volcanoes, copper itself is not the result of an earthly geologic process. It predates the Earth’s geologic timescale. But concentrations of it are found in rock formations in places such as the Oquirrh Mountains in Utah, site of one of the world’s largest copper mines (to learn about the elaborate process of extracting copper from earthly materials and transforming it into everyday objects, such as cell phones, watch this Rio Tinto corporate video).

If we were to date the materiality of the Prospect Park panthers for Geologic City, we’d have to call it something that signaled the fact that their copper predates the formation of the Earth. It’s “pre-Earthian.” But, we’re using the official geologic timescale for our project, and that begins with Earth time. Earth’s earliest history is known informally as the “Precambrian.” This supereon makes up 87% of Earth’s geologic history. So, because the copper of the panthers–along with all of the other natural elements–is made out of materialities present at the formation of the Earth, in the language of the geologic timescale, it “dates to” the earliest of the Precambrian.

The panthers stand on pedestals designed by Stanford White (an architect who also designed the Washington Square Arch). The pedestals are made of material that is ubiquitous throughout the city: Indiana limestone. Indiana limestone’s place in the geologic timescale is a serious warp forward from the copper of the panthers. The limestone dates roughly to a mere 359 to 318 million years ago, or the Mississippian. If you need a reminder of where that falls within the geologic timescale check-out our Geologic Time Viewerfor a refresher.

New York’s infrastructure could flow nowhere without manhole covers, they are crystallized instances of the human and the geologic converging in the City. These holes, descending to depths of over 800 feet, are points of admittance to the City’s subterranean infrastructural realm. The covers conceal access to millions of miles of cable and tunnels for water, steam, gas, subways, water and sewer. Each cover signifies an entry into another level of urban flow taking place under and throughout the City. At the street level, the sheer quantity and variety of manhole covers is incredible. There are over 600,000 of these cast iron caps, weighing between 300 to 500 pounds, scattered throughout New York. Many are imprinted with beautiful patterns or long-gone names and addresses. The iron? Another “pre-Earthian” element dating to the earliest stages of the Earth, over 4.6 billion years ago.

We were particularly intrigued by the manhole cover pictured above. New York City manholes are manufactured in India? We found identical covers at the end of every long cross-town Avenue that we walked that afternoon. Apparently Indian manhole covers have been phased out in recent years due to a change in the City’s design specifications. But a 2007 article in the New York Times details how these covers were forged worlds away, under highly precarious work conditions.

After only one week of Geologic City research, we realize that our project is going to be more complex than we had imagined. Apparently, we’ll be gaining vivid, embodied senses of many technical and scientific details, personal histories, city and governmental agencies, and far flung connections, all interwoven within New York City as we pursue our search for its geologic roots.

I love what the FOP team is doing with this site. This is a great report on NYC’s geology. However, there are a couple of corrections I would make to the narrative here, from the perspective of a nit-picky east coast geologist :) —

You said “Manhattan schist, part of the solid bedrock support responsible for making skyscrapers possible on Manhattan, formed about 450 million years ago. Back then, it was part of the super continent Pangea. The schist is the second oldest component of New York City’s bedrock, after Fordham Gneiss. The schist became part of Manhattan island during continental collision between the floor of the Atlantic Ocean and the East Coast of North America.”

There are several errors in this paragraph. Here are my tweaks:
The Manhattan schist was metamorphosed 450 million years ago, but metamorphic rock comes from other rock, so the original rock is older than 450 Ma, though we can’t say how much older. The process of subduction that closed the predecessor to the Atlantic Ocean (and made Pangea) began around 450 Ma with a series of smaller scale collisions, but Pangea itself didn’t form until about 300 Ma. If you want the gory details, it goes something like this:
OLDEST Taconian Orogeny ~450 Ma (caused by collision of North America with a chain of volcanic islands, like modern day Indonesia)
MIDDLE Acadian Orogeny ~360 Ma (caused by collision of North America with a micro-continent, like modern-day Madagascar)
MOST RECENT Alleghanian Orogeny ~300 Ma to ~250 Ma (caused by collision of North America with Africa, the leading edge of the southern supercontinent Gondwana)

The name of the ocean basin that closed, bringing these disparate crustal fragments together was not Atlantic but “Iapetus.” (Check the relationship of Iapetus to Atlas in Greek mythology for a neat tie-in.) When the Iapetus died, Pangea was born. When Pangea died (rifted and broke up), only then was the Atlantic born. The oldest oceanic crust in the Atlantic is ~200 Ma (same age as your brownstones), and that’s less than half the age of the metamorphic bedrock of Manhattan.

Another quibble is with your presentation that “Geologist [sic] call the first epoch of Earth’s history the “Precambrian.”” This is not true. Epochs are subdivisions of periods, and periods are subdivisions of eras, which are subdivisions of eons. Informally, the term “Precambrian” is used to refer to all chunks of time prior to the Cambrian period, but it is neither an official term, nor an “epoch” (nor an “era”).

I offer these comments up in hopes of enriching your future explorations of geology. I’m looking forward to reading more of your adventures and explications!

[…] in the context of of vast timescales. Nine entries have been produced thusfar, including reports on the use of trisassic sandstone in Park slope brownstones, the materiality of the Federal Reserve Bank and its precious holdings, […]

I love this project. May I add a few notes? 1) No visit to the far north of Manhattan should be complete without a mention of Inwood marble. This is the third major type of Manhattan rock. Most of it is buried, but there’s a small outcropping just outside of Inwood Hill Park itself. The marble is a good example of how geology can influence topography. It’s what is under the Harlem Plain, and, easily eroded and weathered, makes good soil — see the Manahatta Project for info on that. And, of course, marble is metamorphosed limestone, which was originally little sea creatures.

2) The Panther Gates at 3rd St., like all the statuary that rings the park, is post Olmsted/Vaux and over their dead bodies, as it were. They didn’t want anything like that in or around their rustic-in-urban park. A nice illustration of how fashion changes; the late 19th C fad for memorials, many for the Civil War, came about a generation after the war, when many of the veterans were on their last legs.